1. Field of the Invention
The present invention relates to a video data processing method, a video data processing apparatus, and a video data recording and reproducing apparatus, in which a video signal is compressed and encoded on a relatively large macroblock and displayed so that, when reproducing the video data recorded on a video tape, the content of the reproduction video can be easily recognized even if when a high speed reproduction or when data error is occurred.
2. Description of the Related Art
In general, digital video data of a moving picture has been compressed and coded by dividing the video data contained in each of the frames into relatively small blocks, each consisting of, for example, 8.times.4 pixels and performing processing such as predictive coding in units of these blocks. At present, however, large macroblocks of, for example, 16.times.16 pixels are now being used for the compression and coding of video data.
In order to prevent a burst-like data error from occurring at the reproduction and the error correction processing from becoming impossible due to occurrence of a large amount of error in the error correction data block (ECC block) by the same error correction code, the video data is recorded on a magnetic tape for video tape recorder (VTR tape) with the video data shuffled so that the distribution of the large macroblocks contained in the same ECC block becomes random on the helical tracks of the VTR tape.
No problem occurs when reproducing at a usual (normal) reproduction speed the video data compressed and coded using large macroblocks and recorded on the VTR tape shuffled so that the distribution on the helical tracks becomes random as explained above. However, it is sometimes desired to reproduce such video data from the VTR tape at a high speed such double speed or triple speed. At high speed reproduction, the reproduction head of the video cassette recorder (VCR) does not scan (trace) along the helical tracks of the VTR tape, but traces the helical tracks at an angle in accordance with a speed, which is a predetermined times of a normal speed, for the high speed reproduction with respect to the longitudinal direction of the helical tracks. Accordingly, all of the video data recorded on each of the helical tracks are not reproduced at the high speed reproduction--only one part is reproduced.
In the conventional shuffling, the video data is shuffled so that the distribution of the macroblocks contained in the same frame becomes constant on the helical tracks of the VTR tape, therefore where only part of the video data recorded on each of the helical tracks is reproduced, macroblocks spaced apart from each other on the image are reproduced from the same helical track.
When the macroblock is relatively small, due to the properties of human vision, the individual macroblocks which are reproduced do not stand out and the entire image appears integrated, therefore there is a little effect exerted upon the viewer. However, the larger the macroblock, the more the individual macroblocks stand out and harder the reproduced image becomes to be viewed by the viewer. That is, in such a case, a plurality of rectangular areas (macroblocks) spaced apart from each other are reproduced at random and the image appears unnatural to the viewer as if it were divided into separate areas like a checkered flag. Such a phenomenon becomes conspicuous when the motion of the video is vigorous.
Usually a plurality of recording magnetic heads and reproduction magnetic heads (recording/reproduction heads) are respectively disposed on a tape travelling surface of a rotation drum of a video cassette tape recorder for recording and reproducing (recording/reproducing) digital audio data and digital video data of a moving picture (audio and video data). These magnetic heads respectively scan specific helical tracks on the VTR tape to record and reproduce the shuffled audio and video data.
The disadvantages, for example, clogging of a magnetic head (head clogging), sometimes occurs in one or more of the plurality of recording/reproduction heads of the tape traveling surface of the rotation drum of the VCR. In such a case, the recording and reproduction of the audio and video data recorded on the helical tracks corresponding to the recording/reproduction head in which trouble is caused continuously become impossible. Accordingly, a loss of image continuously occurs at the same position over the frames and cannot be corrected by interpolation on a time axis using the video data of this other frames. That is, for loss of image due to head clogging etc., it is necessary to interpolate and correct the loss by using the other video data in the same frame.
However, when recording/reproducing video data shuffled by a pattern so that the video data recorded and reproduced by one scan of the recording/reproduction heads are collected together so as to correspond to a wide range of the screen, the area of the loss of the image due to head clogging etc. becomes large and interpolation in the same frame becomes impossible.
Alternatively, it can be considered to use a powerful error correction code (ECC) having a high error correction ability so as to correct the loss of image due to head clogging etc. When adopting this method, however, the amount of data of the ECC code having a high error correction ability is large, and the proportion of it occupying the audio and video data becomes high, therefore it will prevent efficient recording of the audio and video data.